In recent years, a liquid crystal display device (LCD) has been widely used because of its thinness, lightweight and low power consumption. The liquid crystal display device contains a liquid crystal cell and a polarizing plate. The polarizing plate is usually composed of a protective film and a polarizing film and is obtained by dyeing a polarizing film formed from a polyvinyl alcohol film with iodine, stretching the film, and stacking a protective film on both surfaces thereof. In a transmission-type liquid crystal display, this polarizing plate is attached to both sides of a liquid crystal cell and one or more optical compensation sheets are sometimes further disposed thereon. Also, in a reflection-type liquid crystal display device, a reflector, a liquid crystal cell, one or more optical compensation sheets and a polarizing plate are usually disposed in order.
LCD is not a self-light-emitting type display device and requires a surface light source. As for the form of the surface light source, a backlight type where a uniform surface light source is obtained by placing a member having a light diffusing ability, such as diffusion sheet or prism sheet, to intervene between a liquid crystal cell and a light emission source, is widely used, and a cold-cathode tube (CCFL) or LED is used as the light emitting source. Also, in some LCD, there is known a type where a light source is disposed in the edge part of a light guide plate and combined with a diffusion sheet, a prism sheet or the like to work as a surface light source (edge light type). In these types, generally, a line light source or a point light source is converted into a surface light source as described above and therefore, a uniform surface light source is obtained using a diffusion sheet.
Out of the members of a backlight for obtaining a surface light source, the diffusion sheet is generally disposed between a backlight and a polarizing plate on the backlight side. By disposing a diffusion sheet, reduction of luminance unevenness and surface uniformization of display characteristics are achieved (JP-A-2000-75134 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)) and at the same time, production of an interference fringe such as moiré due to interference of incident light with a pixel in the liquid crystal cell can be suppressed.
However, attempts are being recently made to decrease the number of members of a liquid crystal display device or for affording low power consumption, to decrease the number of fluorescent lamps utilized as the light source. In addition, since thinning of LCD allows for a small distance between the backlight source and the diffusion sheet, it becomes difficult for a conventional diffusion film to achieve uniform light diffusion. Accordingly, in order to gain the distance as much as possible, a backlight-side polarizing plate having diffusibility on its surface has been put into use as a substitute for the diffusion sheet.
For example, in JP-A-2000-75134, a light-diffusive polarizing plate with a light diffusion layer having predetermined properties and containing a porous amorphous particle and a spherical particle in a dispersed state has been proposed, and it is disclosed that a light diffusion sheet can be thereby dispensed with. Also, in JP-A-2001-172403 and JP-A-2003-25504, a production method of a light diffusion film, including casting a fine particle-containing dope on a support, has been proposed, and it is disclosed that according to this method, a light diffusion film excellent in the optical isotropy and the like can be obtained.
In addition, it has been proposed that an ellipsoidal particle can be used for a film having light diffusibility. For example, in JP-A-2000-258612, a forward scattering film containing a flat particle (a particle in a rotated ellipsoidal, discotic, rugby-ball or the like shape) is described, and it is disclosed that when this film is incorporated into a reflection type liquid crystal display device, the forward scattering function and visibility are greatly enhanced. In JP-A-2001-281402, as regards an antiglare film comprising a transparent support having formed thereon an antiglare layer, where the apex angle of the antiglare layer surface is specified, an embodiment using a flat particle is described, and it is disclosed that an antiglare film ensuring little whitish tint and high sharpness of transmitted image is obtained. In JP-A-2008-287072, it is disclosed that when a flat translucent particle is used in a hardcoat layer composed of a curable resin and an aggregating inorganic particle is used in combination, an antiglare film assured of antiglare property and front contrast and free from glaring can be obtained.